This invention is generally directed to photoresponsive devices, and more specifically the present invention is directed to photoresponsive imaging members, including layered members, containing certain perylene dye compositions. Thus, in one embodiment, the present invention envisions the use of certain perylene dye aggregate compositions as organic photoconductive materials in photoresponsive devices, in combination with specific hole transport layers. In one important feature of the present invention the imaging member is ambipolar, that is it can be charged either positively, or negatively. Photoresponsive devices containing the perylene compositions disclosed in combination with amine hole transport substances are useful in electrophotographic imaging systems, especially xerographic systems, wherein negatively charged, or positively charged images are developed with toner compositions of the appropriately charge.
Numerous different xerographic photoconductive members are known including, for example, a homogeneous layer of a single material such as vitreous selenium, or a composite layered device containing a dispersion of a photoconductive composition. An example of one type of composite xerographic photoconductive member is described for example, in U.S. Pat. No. 3,121,006, wherein there is disclosed finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. The binder materials disclosed in this patent comprise a material which is incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. Accordingly, as a result, the photoconductive particles must be in a substantially contiguous particle-to-particle contact throughout the layer for the purpose of permitting charge dissipation required for a cyclic operation. Thus, with the uniform dispersion of photoconductive particles described, a relatively high volume concentration of photoconductor material, about 50 percent by volume, is usually necessary in order to obtain sufficient photoconductor particle-to-particle contact for rapid discharge. This high photoconductive loading can result in destroying the physical continuity of the resinous binder, thus significantly reducing the mechanical properties thereof. Illustrative examples of specific binder materials disclosed in the U.S. Pat. No. 3,121,006 include, for example, polycarbonate resins, polyester resins, polyamide resins, and the like.
There are also known photoreceptor materials comprised of inorganic or organic materials wherein the charge carrier generating, and charge carrier transport functions, are accomplished by discrete contiguous layers. Additionally, layered photoreceptor materials are disclosed in the prior art which include an overcoating layer of an electrically insulating polymeric material. However, the art of xerography continues to advance and more stringent demands need to be met by the copying apparatus in order to increase performance standards, and to obtain higher quality images. Also, there are desired layered ambipolar photoresponsive imaging members.
Recently, there have been disclosed other layered photoresponsive devices including those comprised of separate generating layers, and transport layers, reference U.S. Pat. No. 4,265,990, and overcoated photoresponsive materials containing a hole injecting layer, overcoated with a hole transport layer, followed by an overcoating of a photogenerating layer, and a top coating of an insulating organic resin, reference U.S. Pat. No. 4,251,612. Examples of photogenerating layers disclosed in these patents include trigonal selenium and phthalocyanines, while examples of transport layers illustrated include certain diamines. The disclosures of each of these patents, namely, U.S. Pat. Nos. 4,265,990 and 4,251,612, are totally incorporated herein by reference.
Many other patents are in existence describing photoresponsive devices including layered devices containing generating substances, such as U.S. Pat. No. 3,041,167, which discloses an overcoated imaging member containing a conductive substrate, a photoconductive layer, and an overcoating layer of an electrically insulating polymeric material. This member is utilized in an electrophotographic copying method by, for example, initially charging the member, with an electrostatic charge of a first polarity, and imagewise exposing to form an electrostatic latent image which can be subsequently developed to form a visible image. Prior to each succeeding imaging cycle, the imaging member can be charged with an electrostatic charge of a second polarity, which is opposite in polarity to the first polarity. Sufficient additional charges of the second polarity are applied so as to create across the member a net electrical field of the second polarity. Simultaneously, mobile charges of the first polarity are created in the photoconductive layer such as by applying an electrical potential to the conductive substrate. The imaging potential which is developed to form the visible image, is present across the photoconductive layer and the overcoating layer.
There is also disclosed in Belgium Pat. No. 763,540, an electrophotographic member having at least two electrically operative layers, the first layer comprising a photoconductive layer which is capable of photogenerating charge carriers, and injecting the carriers into a continuous active layer containing an organic transporting material which is substantially non-absorbing in the spectral region of intended use, but which is active in that it allows the injection of photogenerated holes from the photoconductive layer and allows these holes to be transported through the active layer. Additionally, there is disclosed in U.S. Pat. No. 3,041,116, a photoconductive material containing a transparent plastic material overcoated on a layer of vitreous selenium contained on a substrate.
Furthermore, there is disclosed in U.S. Pat. Nos. 4,232,102 and 4,233,383, photoresponsive imaging members comprised of trigonal selenium doped with sodium carbonate, sodium selenite, and trigonal selenium doped with barium carbonate, and barium selenite or mixtures thereof.
Additionally, the use of squaraine pigments in photoresponsive imaging devices is known, reference, for example, the disclosure contained in a co-pending application wherein there is described an improved photoresponsive device containing a substrate, a hole blocking layer, an optional adhesive interface layer, an organic photogenerating layer, a photoconductive composition capable of enhancing or reducing the intrinsic properties of the photogenerating layer, and a hole transport layer. As photoconductive compositions for this device there can be selected various squaraine pigments, including hydroxy squaraine compositions. Moreover, there is disclosed in U.S. Pat. No. 3,824,099, certain photosensitive hydroxy squaraine compositions. According to the disclosure of this patent the squaraine compositions are photosensitive in normal electrostatographic imaging systems.
The use of certain selected perylene pigments as photoconductive substances is also known. There is thus described in Hoechst, European Patent Publication No. 0040402, BE3019326, filed 5/21/80, the use of N,N'-disubstituted perylene 3,4,9,10, tetracarboxyl diimide pigments as photoconductive substances. Specifically there is disclosed in this publication dual layered photoreceptors, with improved spectral response in the wavelength region of 400 to 700 nanometers containing evaporated N,N'-bis(3-methoxypropyl)perylene-3,4,9,10 tetracarboxyldiimide. It is important to note that these perylenes are insoluble pigments, accordingly photoconductive devices with such compositions must be prepared by costly and complex vacuum evaporation techniques. A similar disclosure is contained in Ernst Junther Schlosser, Journal of Applied Photographic Engineering, Vol. 4, No. 3, page 118 (1978). Also dual layered photoreceptors prepared from the perylene pigments as described in the above mentioned No. 0040402 publication can only be charged negatively thus requiring the use of positively charged toner compositions.
Moreover, there is disclosed in U.S. Pat. No. 4,419,427 electrophotographic recording mediums with a photosemiconductive double layer comprised of a first layer containing charge carrier producing dyes, and a second layer containing one or more compounds which are charge carrier transporting materials when exposed to light wherein perylene diimides are employed as the charge carrier producing dyes, reference the disclosure in Column 2, beginning at line 50. Also of interest is the background information included in Columns 1 and 2 and particularly in Column 2, beginning at line 20 wherein perylene dyes of the formula as shown are illustrated, which dyes are substantially similar to the dyes selected for the photoresponsive devices of the present invention. Examples of charge carrier transporting compounds disclosed in the U.S. Pat. No. 4,419,427 include pyrazoline derivatives, oxazoles materials, triphenylamine derivatives, carbazole derivatives, and pyrene derivatives, as well as other materials, reference the disclosure in Column 4, beginning at line 1.
While photoresponsive imaging members containing the abovedescribed compositions may be suitable for their intended purposes, there continues to be a need for the development of improved members or devices, particularly layered devices. Additionally, there continues to be a need for imaging members comprised of specific amine charge transport compositions and perylene dye photogenerating materials possessing desirable sensitivity, low dark decay, high charge acceptance values, and wherein these members can be used for a number of imaging cycles in a xerographic imaging apparatus, or in printing devices. Further, there continues to be a need for photoresponsive devices which are ambipolar, thus permitting both normal and reverse copying of black and white, or color images. These devices which generate both positive and negative charges, that is both holes and electrons, can be repeatedly used in a number of imaging cycles without deterioration thereof from the machine environment or surrounding conditions. Moreover, there continues to be a need for improved layered imaging members wherein the materials selected are substantially inert to users of these members. Furthermore, there continues to be a need for layered device which can be charged positively only, negatively only, or are ambipolar. Also, there continues to be a need for photoconductive materials which can be fabricated into imaging devices by simple coating techniques, and wherein these materials are preferably soluble in common coating solvents, and are compatible with the resinous binder resins selected.